1. Field of the Invention
The present invention relates to a motor and a wiper apparatus having the same.
2. Description of Related Art
For example, Japanese Unexamined Patent Publication Number 2005-94821 discloses a motor that is used as a drive source of a vehicle wiper apparatus. With reference to FIG. 6, this motor includes a motor unit 50 and a speed reducer 55. The motor unit 50 is rotated to rotate a rotatable shaft 51, to which a worm 51a is formed integrally. The speed reducer 55 is connected to the motor unit 50 and reduces a rotational speed of rotation transmitted from the rotatable shaft 51. Specifically, the speed reducer 55 has a speed reducing mechanism, which includes the worm 51a and a worm wheel 57 received in a gear housing 56 that is connected to the motor unit 50. When the worm 51a and the worm wheel 57 are rotated upon rotation of the motor unit 50, an output shaft 58, which is fixed to the worm wheel 57, is rotated to rotate a crank arm 60 of a link mechanism. Then, the rotation of the crank arm 60 is converted into reciprocal swing movement of wipers (not shown) through the link mechanism.
A base end portion of the output shaft 58 is fixed to a center part of the worm wheel 57, and a distal end portion of the output shaft 58 extends outward through a cylindrical shaft support 56a, which projects from an outer surface of the gear housing 56. One end portion of the crank arm 60 is connected to the projected distal end portion of the output shaft 58. A cylindrical bearing 59 is fixed to an inner peripheral surface of the shaft support 56a, and an intermediate portion of the output shaft 58 is rotatably supported by the bearing 59.
However, the output shaft 58 is fixed to the center part of the worm wheel 57 only at the one axial end portion and is supported by the bearing 59 on one side of the worm wheel 57. An axial extent of the bearing 59 is displaced from an axial extent of an engaging part 57a, which is provided at an outer peripheral part of the worm wheel 57, when they are viewed in a direction perpendicular to an axis Lc of the output shaft 58. Particularly, a straight line Ld, which is perpendicular to the axis Lc of the output shaft 58 and passes through a contact point (pitch point) P12 between the worm 51a and the worm wheel 57, is axially largely displaced from an axial support range B of the bearing 59.
Thus, when the load (wipers) is driven by rotating the output shaft 58, the output shaft 58 may possibly be tilted in some cases. The tilting of the output shaft 58 is particularly notable in the above case where the crank arm 60 is driven by the output shaft 58. In such a case, the output shaft 58 is tilted about a fulcrum P11, which is located at an axial center point of the bearing 59 along a central axis of the bearing 59. Thus, when the worm wheel 57, the output shaft 58 and the bearing 59 are arranged in the above described manner, a distance L11 between the fulcrum P11 and the contact point P12 becomes relatively long. This poses the following disadvantage. That is, the tilting of the output shaft 58 causes a signification change in an engaged state between the engaging part 57a of the worm wheel 57 and the worm 51a. This will result in disadvantages, such as generation of noise as well as increased frictional wearing at the engaged part between the engaging part 57a of the worm wheel 57 and the worm 51a. 
Furthermore, it should be noted that the output shaft 58 could be also tilted about the fulcrum P11 by an urging force, which is generated by the rotation of the worm 51a to push the worm wheel 57 in a direction away from the worm 51a. In such a case, when the distance L11 between the contact point P12 and the fulcrum P11 is relatively long, the load, which is applied to the bearing 59 to tilt the output shaft 58, is disadvantageously increased. This may cause an increase in sliding noise generated from the bearing 59 and an increase in frictional wearing of the bearing 59.